The present invention generally relates to corrosion protection systems and, more particularly, to corrosion protection for magnesium materials using an adhesion promoter.
The use of magnesium and magnesium alloy parts in vehicles is common due to the lightweight qualities of magnesium and the ease of casting the metal. As such, parts such as gearboxes for vehicles such as fighter aircraft and helicopters are often made using magnesium. This metal, however, does not come without its drawbacks. Magnesium corrodes much more easily than other metals used for vehicle parts. Water and salt from rain, salt fog or salt spray can have a negative corrosive affect on parts made of magnesium. As a result, these magnesium parts must be serviced or replaced more often than parts made from other metals. Consequently, vehicles and components that include magnesium parts can experience line shortages or suspensions as the parts are serviced or replaced. Corroded magnesium parts typically go through a repair process wherein corroded areas of the magnesium parts are removed or abraded and the remaining surface is treated with anti-corrosion or corrosion-inhibiting substances.
One approach to the corrosion problem is to use a chromate conversion process to treat the surfaces of magnesium parts that are prone to corrosion. Chromate conversion processes introduce chromium into the outer surface of magnesium parts. Chromium possesses anti-corrosion properties and therefore aids in the purpose of fighting corrosion in magnesium parts. The chromate conversion process does not keep out those elements that cause corrosion; it simply inhibits corrosion along the treated surfaces of the magnesium parts.
Another approach to the problem of corrosion in magnesium parts is to apply a resin seal on those magnesium parts that corrode easily. Resin seals provide an outer shell and waterproof seal that helps to repel and keep out those atmospheric elements that cause corrosion, such as water and salt. Thus, resin seals provide a measure of corrosion resistance to magnesium parts. Resin seals, however, simply keep out those elements that cause corrosion; they do not inhibit corrosion on magnesium surfaces.
Yet another approach to the problem of corrosion in magnesium parts includes the use of both a chromate conversion process and resin seals. In this approach, the affected magnesium parts undergo the chromate conversion process and subsequently a resin seal is applied over the chromate surfaces. Observations, however, show low wet adhesion between the resin seal and the chromate surface coating, leading to peeling or blistering of resin seal and corrosion of the magnesium substrate. Thus making this combination of elements inadequate for corrosion resistance.
As can be seen, there is a need for an improved corrosion protection system that both inhibits corrosion in magnesium parts and denies entry of corrosive materials into magnesium materials. Moreover, there is a need for a method for repairing corroded magnesium parts by removing existing corrosion and restoring corrosion resistance in order to place the parts in a proper form for reuse.